1. Field of the Invention
The present invention relates to a magnetic circuit that generates magnetic resonance in an object.
2. Description of the Related Art
Within a living body, reactive oxygen species are generated due to external factors such as radiation and ultraviolet rays or internal factors such as hypoxia and inflammation. Therefore, precisely measuring free radicals such as reactive oxygen species in the body are important for the people's health and welfare such as evaluation and creation of antioxidant medicines and the like.
Japanese Patent Application Laid-Open Publication No. 2006-204551 (Patent Document 1, hereinafter) describes a measurement instrument that performs a measurement necessary for obtaining information on free radicals within an animal body. In the measurement instrument, a first external magnetic field generation device for ESR (Electron Spin Resonance) excitation and a second external magnetic field generation device for MRI (Magnetic Resonance Imaging system) excitation apply a magnetic field to a coil that moves in a linear direction. The ESR is a method of obtaining information on free radicals within a living body accommodated in a coil by measuring a signal generated by electron spin resonance. On the other hand, the MRI is a method of obtaining information on the form of a living body by measuring a signal generated by nuclear magnetic resonance. Thereby, the measurement instrument supplements the functional information on free radicals obtained by the ESR with the information obtained by the MRI and obtains information on free radicals in the animal body. Moreover, the measurement instrument of Patent Document 1 is used also as a nuclear-electron multiple magnetic resonance measurement instrument that causes a transition of the electron spin in a living body by the Overhauser effect, causes an energy transition on the nuclear spin and displays a functional image and a morphological image of each part within the living body.
In addition, Japanese Patent Application Laid-Open Publication No. 2010-227247 (Patent Document 2, hereinafter) discloses a technology of applying a first magnetic field for ESR measurement and a second magnetic field for MRI measurement to a moving coil mounted on a rotary table.
In order for a measurement instrument to perform ESR measurement with high sensitivity, it is desired to apply a uniform magnetic field for a rather long time and sufficiently excite the electron spin in the living body. However, when the relaxation time after the electron spin excitation is considered, since it is more desirable to perform the MRI excitation at a short time interval after the ESR excitation, the rotation speed of the rotary table cannot be decreased. Therefore, since it is necessary that the uniform magnetic field space be large, a plurality of disk-shaped magnets are provided so as to be juxtaposed to each other in the first external magnetic field generation device.